The present invention is generally concerned with apparatuses for cleaning thin substrates such as semiconductor wafers, compact discs, flat panel displays and the like. More particularly, the invention is concerned with brush apparatuses for cleaning thin substrates.
For fabrication of semiconductor devices, thin slices or wafers of semiconductor material require polishing by a process that applies an abrasive slurry to the wafer""s surfaces. After polishing, slurry residue is generally cleaned or scrubbed from the wafer surfaces via mechanical scrubbing devices, such as brushes made from porous or sponge-like material.
A brush apparatus for cleaning disks is described in co-pending U.S. patent application Ser. No. 09/580,879, filed May 30, 2000 and assigned to the present assignee, entitled xe2x80x9cBrush Core for Disk Scrubbing Apparatus and Method for Use Thereofxe2x80x9d. The teachings of this prior application are incorporated herein by reference.
FIG. 1 is a schematic side perspective view of a scrubbing device 10 for wafer cleaning of the type disclosed in the above-referenced prior patent application. The scrubbing device 10 includes first and second brush rollers, 13a and 13b, which are positioned to contact both sides of a wafer W. A known mechanism 17, such as a motor, is operatively coupled to the first and second brush rollers, 13a and 13b, so as to selectively rotate the first and second brush rollers, 13a and 13b. Also, the wafer W is supported on rotating wheels 19a-19c for both supporting and rotating the wafer W.
In operation, the first and second brush rollers 13a and 13b are initially in an open position, at a sufficient distance from each other so as to allow a wafer to be inserted therebetween. Thereafter, the wafer W to be cleaned is positioned on the rotating wheels 19a-c between the first and second brush rollers, 13a and 13b, and the brush rollers assume a closed position, sufficiently close to each other so as to both hold the wafer W in place therebetween and to exert a force on the wafer surfaces adequate to achieve effective cleaning.
The motor 17 causes the first and second brush rollers, 13a and 13b to spin. Preferably the brush rollers spin in opposite directions, as indicated by arrows S1 and S2 in FIG. 1 applying forces to the wafer in a downward direction while the wafer rotates, so as to drive the wafer into the rotating wheels 19a-19c so that the wafer remains engaged by the rotating wheels.
While the pair of brush rollers spin, the rotating wheels 19a-19c which engage the wafer""s edge rotate causing the wafer to rotate. Rotation of the wafer W helps to ensure that the pair of brush rollers thoroughly contact and clean the entire surface of the wafer W. In addition, a cleaning liquid such as de-ionized water is supplied to the wafer surface through perforations in the brush surface to assist in the removal of contaminants.
In FIG. 1, the brushes 13a and 13b have been schematically illustrated as positioned against the wafer W without supporting structure for mounting the brushes. However, as will be recognized by those who are skilled in the art, in a practical embodiment of a wafer scrubber, there must be provided suitable mechanisms for rotatably mounting the brushes in place, transmitting rotary motion to the brushes from a motor, and supplying cleaning liquid to the brushes. According to known techniques, each brush is mounted on a rigid core and a respective mounting assembly is provided to rotatably support each end of the rigid core. One of the mounting assemblies may be motor driven to impart motion to the rigid core and the mounted brush via the driven mounting assembly. The portion of the other mounting assembly which is connected to the rigid core has rotary motion transmitted thereto by the rigid core. It is known to supply cleaning liquid to the brush through the mounting assembly that is not motor driven.
In accordance with conventional practice, the portion of the mounting assembly that rotates with the brush is mounted on a bearing. Reliable and satisfactory operation of the scrubbing device requires that the cleaning liquid be kept away from the bearing. If the cleaning liquid were to reach the bearing, it could degrade the performance of the bearing, and also could result in lubricant from the bearing being transmitted to the wafer. For that reason, it is known to provide a seal between the source of the cleaning liquid and a bearing assembly. However, the seals that have been used in conventional brush mounting assemblies have been found to be a source of particle contamination. Moreover, such seals tend to degrade and leak over time, leading to bearing breakdown and contamination of the wafer by lubricant from the bearing.
In accordance with the invention, a mounting assembly for a wafer-scrubber brush includes a first tube that is fixedly mounted and has a bore in which a cleaning liquid flows, and a second tube having a bore in which the first tube is inserted. The inventive mounting assembly includes at least one bearing adapted to mount the second tube for rotational motion, and a housing in which the at least one bearing is fixedly mounted. Further included in the inventive mounting assembly are an assembly block in which the housing is mounted, and a first shield mounted on the second tube and adapted to rotate with the second tube. The first shield defines a gap between the first shield and the housing, and the gap is dimensioned so as to discourage flow of the cleaning liquid in the gap.
Further in accordance with the invention, the mounting assembly may include a drainage opening formed in the assembly block and extending downwardly from a location adjacent the first shield.
The first shield, which is rotationally mounted with the second tube, forms a virtual or labyrinth seal relative to the housing in which the bearing is mounted. Because the seal is virtual, and is therefore not in contact with the housing, this virtual seal does not generate particles which may contaminate the wafer. At the same time, the cleaning liquid is kept away from the bearing so that the life of the bearing is not shortened, and there is no contamination of the wafer by the bearing lubricant.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims, and the accompanying drawings.